Continuous casting apparatus with temperature control including successive layers of material

ABSTRACT

A method and apparatus for continually casting molten metal in solid lengths such as rods, tubes, etc. whereby liquid molten metal such as copper is forced from a reservoir through a nozzle having a cross-sectional area which decreases, as the molten metal flows through the nozzle and solidifies, to account for the volumetric change resulting from the liquid to solid phase transformation of the metal. The nozzle is surrounded by layers of fused compounds which have successively lower melting points to optimize heat flow. The position and profile of the liquid solid interface within the nozzle can be altered as described below by controlling the temperature of the liquid metal entering the nozzle as well as the temperature in the nozzle and controlling the pressure of the liquid metal continuously entering the nozzle.

United States Patent McAlister [63] Continuation-impart of Ser. No.868,756, Oct. 23,

1969, abandoned.

[52] US. Cl. 164/283, 164/89 [51] Int. Cl 822d 11/12 [58] Field ofSearch 164/81, 82, 89, 273 R, 164/283; 425/67 [56] References CitedUNITED STATES PATENTS 2,131,307 9/1938 Behrendt 164/273 R 2,363,69511/1944 Ruppik 164/81.

3,430,680 3/1969 Leghorn 164/81 CONTINUOUS CASTING APPARATUS WITHTEMPERATURE CONTROL INCLUDING SUCCESSIVE LAYERS OF MATERIAL Roy E.McAlister, 5285 Red Rock North, Phoenix, Ariz. 85018 Filed: May 23, 1972Appl. No.: 256,165

Related U.S. Application'Data I Inventor:

Primary Examiner-R. Spencer Annear Att0rney.l0hn W. Malley, Raymond F.Lippitt et '31.

[57] ABSTRACT A method and apparatus for continually casting molten 7metal in solid lengths such as rods, tubes, etc. whereby liquid moltenmetal such as copper is forced from a reservoir through a nozzle havinga cross-sectional area which decreases, as the molten metal flowsthrough the nozzle and solidifies, to account for the volumetric changeresulting from the liquid to solid phase transformation of the metal.The nozzle is surrounded by layers of fused compounds which havesuccessively lower melting points to optimize heat flow. The positionand profile of the liquid solid interface within the nozzle can bealtered as described below by controlling the temperature of the liquidmetal entering the nozzle as well as the temperature in the nozzle andcontrolling the pressure of the liquid metal continuously entering thenozzle.

13 Claims, 4 Drawing Figures PATENTEDSEP 4m: v 375 3 5 2%) .5. M41AS77576 M Q/ZAW ATTORNEYS PATENTEDSEP 4 ms SHEET 2 0i 2 ATTORNEYS 1CONTINUOUS CASTING APPARATUS WITH TEMPERATURE CONTROL INCLUDINGSUCCESSIVE LAYERS OF MATERIAL This application is a continuation-in-partof Ser. No. 868,756 filed Oct. 23, 1969 (now abandoned).

BRIEF DESCRIPTION OF THE PRIOR ART AND SUMMARY OF THE INVENTION overmany centuries a number of distinct advantages over other metal formingmethods including the ability to form extremely complex objects ofvirtually unlimited size and having a variety of isotropic propertiesnot possible with other techniques such as cold working or 2 extrusion.

One of the major disadvantages of casting metal in a stationary mold,however, is that a cumbersome number of time-consuming and frequentlydifficult steps must be carried out before a finished product isproduced, including adding the metal to the mold, cooling the metal inthe mold under whatever conditions are necessary to achieve satisfactorysolidification and then removing the object from the mold after it hassoliditied and cooled. Even if the mold can be reused, its output offinished objects in a given time is extremely low compared to othermetal working techniques such as cold or hot extrusion. One techniquewhich has been used in the past to increase this output and to combinethe advantages of casting with the advantages of fast processes such asextrusion in forming solid lengths of rods, pipes, etc., is termedcontinuous casting and in this technique molten metal is continuallyforced through an aperture or tunnel which is formed in a suitable solidstructure such as a die. The molten metal is also cooled as it is forcedthrough the aperture or tunnel so that a solid length of metal iscontinually formed and emerges from the aperture or tunnel. Thiscontinuous casting technique requires much-less production supervisionto produce a given amount of final product than conventional castingtechniques using conventional molds, and moreover can form lengths at arapid rate. Even further, in comparison with extrusion processes, thetotal energy consumption for the final product, which may be a rod,tubing, wire, bar, pipe or other asymmetrical and symmetrical shape, isconsiderably less, since no energy is necessary to reheat the moltenmetal after it has solidified for extrusion, nor is any energy expendedin cold working or otherwise fabricating and heat treating the solidmetal.

However, continuous casting processes have not been totally successfulin the past, in part because of the large capital investment required toset up a continous casting operation and also because the characteristics of the final product have not been satisfactory in several ways.Other methods of casting which are more expensive have been able toproduce more satisfactory products. A number of different approaches toimproving continuous casting techniques and devices have been tried inthe past and the US. Fat. to Conlon et al., No. 3,284,859, discloses onesuch approach. The patents to Hornak et al., 3,125,440, Ruppick,2,363,695

and Eldred, 2,242,350 disclose other continuous casting devices.

The present invention relates to a continuous casting arrangement andmethod whereby molten metal is forced through and solidified in a nozzlehaving a crosssectional area which decreases as the metaltravels throughthe nozzle, forms a solid length which emerges from the nozzle and isthen cut and stored in the usual manner. More particularly, the nozzle,according to the invention of this application is surrounded by layersof fused compounds each layer successively encountered by the metalhaving a lower melting point so that heat flow is generally from thenozzle to the uppermost layer. Moreover, a number of arrangements andmethods are disclosed for controlling the pressure and temperature ofthe molten metal entering the nozzle and in the nozzle to adjust thelocation of the liquid-solid interface in the nozzle, thus allowingcontrol of the char- 0 acteristics of the final product and enabling anumber of variables bearing on those characteristics to be adjusted foroptimum operation.

Other objects and purposes of the invention will become clear fromreading the following detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a continuous castingapparatus for easting a solid rod;

FIG. 2 shows a cross-sectional view of the nozzle of the apparatus ofFIG. 1,

FIG. 3 shows a modification of the arrangement of FIG. 1 whereby thepressure and temperature of the liquid metal entering the nozzle can becontrolled, and

FIG. 4 shows a detailed view of the novel arrangement of FIG. 3 wherebythe temperature is controlled by a succession of layers of fusedcompounds.

DETAILED DESCRIPTION OF THE DRAWINGS Reference is now made to FIGS. 1and 2 which show respectively an arrangement for continuously casting asolid length of rod and a cross-sectional view of the nozzle throughwhich the molten metal passes and in which it solidifies. As shown, theliquid metal flows from a large container 20, which serves as areservoir and which may be made of any material suitable for holding theliquid metal being cast, to the nozzle 22 in the solidifying structure24, which serves as a mold, via a line 26, which like container 20 maybe made of any material suitable for carrying the liquid metal beingcast. The molten metal enters the nozzle 22 in an essentially liquidphase and cools as it passes through nozzle 22 to a solid phase so thata solid length 25 of metal in a rod or other configuration emerges fromthe top of structure 24 to be wound upon a suitable reel and then cut inconventional fashion.

As can be clearly seen in FIG. 2, the cross-sectional area of the nozzle22 is greatest where the molten metal is received from the line 26 anddecreases non-linearly as the liquid metal cools and is forced upwardthrough the structure 24 to emerge as the rod 25. Since the metal entersnozzle 22 as a liquid and exits as a solid, a solid-liquid interfacewill necessarily exist within the nozzle 22 between a solid and liquidphase and, as discussed in greater detail below, the exact location ofthis interface, at least in part, determines the properties of the finaloutput product.

It is well known that, as liquid metal cools, it tends to contract andthis contraction has for centuries been one of the major problems ofcasting in a conventional stationary mold. Moreover, it is believed thatfailure to account for this contraction in previous continuous castingtechniques has been the source of many of the problems which haveprevented widespread acceptance of the technique. The present inventionaccounts for this contraction by tapering the cross-sectional area ofnozzle 22, as shown in FIG. 2, so as to compensate for the volumetricchanges which result from the liquid to solid transformation and so thatthe liquid metal moving through nozzle 22 contracts at substantially thesame rate that the corss-sectional area of nozzle 22 is decreased. Thistaper in nozzle 22 permits a controlled degree of extrusion of the solidphase from nozzle 22 which improves density, grain orientation and themechanical and electrical properties of the solid length 25 forming therod or other shape. Of course, since difierent metals which can be casthave different rates of contraction, it may be desirable to tailor thenozzle shape and cross section to the type of metal being cast, so thateach metal has a nozzle designed specifically for it. Since thearrangement shown in FIG. 1 is designed to operate continuously, onlyone product, for example copper rod, would ordinarily be produced.

It may be desirable to adjust the location of the solidliquid interfacein the nozzle, for example, to make sure that the rate of change of thecross-sectional area of the nozzle conforms closely to the actualvolumetric changes in the liquid to solid transformation or providechanges in certain properties of the output product and this adjustmentmay be made in one or more of a number of ways. First, the pressureapplied to the liquid metal to force it into and through the nozzle 22and accordingly, the pressure within the nozzle 22 may be controlled toadjust the rate of flow of the liquid through the nozzle and hence thecooling rate and the position of the liquid-solid interface. Secondly,the temperature of the liquid metal entering the nozzle as well as therate at which the temperature drops as the liquid moves through thenozzle 22 and is solidified can also be controlled in a variety of waysto shift the liquid solid interface as desired.

The pressure exerted upon the liquid metal entering nozzle 22 can beadjusted in several ways. First, the effective head of the liquid metalabove the nozzle 22 can be controlled. It may be possible to move theliquid reservoir container 20 vertically or to alter the amount ofliquid metal stored therein. Further, as shown in FIG. 1, gas can bepumped into the space above the liquid in container 20 from a source 28and kept at a variable pressure above atmospheric pressure by source 28to exert pressure downward upon the metal in the container 20 which istransmitted to the nozzle. Even further, a suitable pressure exertingdevice 30, shown in FIG. I, can be used to provide additional control ofpressure which is exerted directly upon the liquid metal flowing in theline 26 toward nozzle 22 and that pressure may range from a vacuum to apressure greater than both the atmospheric pressure and the pressureexerted by the gas above the liquid metal in the reservoir container 20.

Reference is now made to FIG. 3 which shows another continuous castingapparatus with a reservoir container 40 similar to the container 20 inFIG. 2. Like container 20, reservoir container 40 may be a holding etyof means. An emergency valve 48 mounted in line 44 between container 40and nozzle 46 is also shown in FIG. 3 and allows the flow of liquidmetal to the structure 42 to be cut off for any reason.

As in the embodiment of FIG. 1, it is contemplated that a source of gaswill be associated with the container 40 so that gas pressure above theliquid in container 40 can be used to at least partially control thelocation of the solid-liquid interface in the nozzle 42. Even further,in this arrangement it is contemplated that more pressure can be addedor subtracted to the liquid metal flowing in the line 44 by an inductionpump 50, which is supplied with energy from a suitable source 51 andwhich generates, by means of the coils 53 wrapped around the line 44, amagnetic field which is orthogonal to electrical current generated inthe fused cooper or other metal flowing in line 44 by a suitableelectrical or similar device. In the arrangement of FIG. 3, even morepressure can be exerted upon the line 44 by a piston arrangement 54 inwhich hydraulic pressure is applied to the liquid metal flowing downline In addition to controlling the location of the liquid solidinterface by applying pressure to the liquid flowing in the line 44, thearrangement of FIG. 3 contemplates that the temperature of the liquidflowing in line 44 as well as the temperature of the liquid in structure42 can be controlled to place the location of the interface so that theproperties of the final product are as desired.

As shown in FIG. 3, the source of electrical energy 51 also forcescurrent to flow through the liquid in the container or line 44. Thiscurrent flowing in the line 44 is acted upon by the induction pump andalso resistively heats both the liquid metal in the container 40 and themetal flowing through the line 44. Moreover, in the arrangement of FIG.3, it is contemplated that nozzle 46, which as mentioned above, issimilar to the nozzle 22, will be kept at essentially a constanttemperature by exchanging heat through a medium 49 of solid and liquidmaterial such as a fused salt. Alternately, temperature control at thenozzle 46 may be accomplished by exchanging heat to a split phase mediumconsisting of gas and liquid phases so that in the gas generated by theheat exchange process is condensed by the heat exchanger at a pointremoved from the nozzle and added back to the bath, thereby stabilizingthe nozzle temperature. A concentric heat exchanger may also be addedaround the device 42 if desired to assist in heat removal.

Further, the nozzle temperature can simply be controlled and furthercooling of the extruded metal accomplished simply by causing the metalto flow through layers of fused compounds such as shown in FIG. 4,

which surround nozzle 60, each higher compound being of a lower meltingpoint so that heat flow is generally caused to be from the nozzle to theuppermost layer. Two or more layers are required and three layers hasbeen found particularly satisfactory. For example, in the arrangement ofFIG. 4, the liquid metal enters the nozzle 60 which may be similar tonozzle 22 from the line 62 and flows in turn through a first layer 64which may be comprised of a first fused salt at the melting point ofl,000 F. through a second layer 66 which may be another fused salt withmelting point of 600 F. and finally through a layer 68 which may, forexample, be of liquid lead.

The following table sets forth a number of specific combinations offused compounds with the first layer being that first encountered by themetal, the second layer being that next encountered, etc.:

First Second Third Other heavy salt systems which can be combinedtogether in layers include mixtures of:

via, 1.,F, NaF, and KP PbF LIF, NaF and KP PbCl,, 1.,cl, NaCl and KClUF, PbCl, and ZnlFl,

L,F and NaF The layers operate to effectively limit the amount of liquidmetal passing through them which can be taken into solution.

The temperature of the liquid flowing in the line 44 may also becontrolled as discussed above and one suitable way of controlling suchtemperature is to simply impinge variable intensity gas flames from thesource 52 onto the line 44 connecting the container 40 to the nozzle 42.Similarly, such control can be accomplished by disposing resistiveelements 54 about the line 44 and controlling the amount of energysupplied to such resistive heaters.

The various control arrangements shown above are capable of producing aproduct which is not only superior in such characteristics as grainrefinement, seamless detail on tubing pipe, and other manufacturalitems, but also results in a remarkable efficiency in producing theproduct at a considerable economy over previous methods of casting. Asmentioned above, the arrangement shown in FIGS. 1-4 in comparison withother methods such as extrusion results in considerably less energyconsumption for the preparation of a variety of products. This energysaving comes about because no reheat energy is required for extrusion,no work energy is encountered in cold working, and no handling energyassociated with competitive fabrications such as annealing and heat upfor heat treating is necessary. Even further, percent inspection is asimple and easy job.

Thus, in comparison with other continuous casting arrangements, thenovel arrangement shown in FIGS. 1-4 is more economical to set up andaccordingly requires less capital investment to produce the sameproducts. Moreoever, any system for producing a given product can benormally converted to produce other products simply by substitutinganother nozzle and making other minor adjustments. Since no water isrequired in this arrangement for cooling the casting, it is believedthat this arrangement will be safer than other continuous castingoperations requiring water.

Another advantage, in comparison with other continuous castingarrangements, is that this system requires no pickling because the finaloutput metal, such as copper rod, can be coated immediately uponexposure to the air.

Accordingly, the advantages of this type of arrangement which not onlyproduces a superior product in comparison with other continuous castingand noncontinuous casting arrangements, but produces that productcheaper, safer and quicker should be apparent; and the scope of theinvention is not intended to be limited only by the scope of theappended claims.

What is claimed is:

1. A continuous casting apparatus comprising:

a source of molten metal,

nozzle means for receiving said molten metal so that said molten metalis transformed from the liquid to solid phase within saidnozzle, saidnozzle having an internal cross-sectional area presented to said moltenmetal which decreases to account for volumetric changes of said metal assaid molten metal travels through said-nozzle means and is transformedfrom the liquid to the solid phase,

.means for conveying said molten metal from said container to saidnozzle, and

means for controlling the temperature of said nozzle means including aplurality of layers about said nozzle means through which said moltenmetal flows, each successive layer encountered being of lower meltingpoint so that heat flow is generally caused to be from said nozzle meansto the layer having the lowest melting point and each having asubstantial thickness sufficient to cool molten metal passing throughsaid nozzle means.

2. An apparatus as in claim 1 wherein said internal cross section variesto account for the volumetric changes in the liquid to solid phasetransformation to improve the density grain orientation and resultingchemical and electrical properties of the product cast.

3. An apparatus as in claim 2 including means for controlling thetemperature of said molten liquid.

4. An apparatus as in claim 3 wherein said temperature control meansincludes means for impinging gas flames on said means for conveying saidmolten metal from said source to said nozzle means.

5. An apparatus as in claim 3 wherein said temperature control meansincludes resistance heating means for heating said conveying means.

6. An apparatus as in claim 3 wherein said temperature control meansincludes an induction heater.

7. An apparatus as in claim 2 including means for controlling thetemperature of said nozzle means.

8. An apparatus as in chaim 2 including means to apply pressure to saidliquid metal to control the location of the liquid-solid interface insaid nozzle means.

9. An apparatus as in claim 8 wherein said pressure control meansincludes means for applying gas pressure to the liquid in said source.

10. An apparatus as in claim 8 wherein said pressure control meansincludes means for applying pressure to liquid in said conveying means.

11. Apparatus as in claim 1 wherein said layers are chosen from thegroup consisting of:

First Second Third Fourth Layer Layer Layer Layer Particularly Pb BiMixture of Graphite useful for UFr, PlJFg Chips steel and LiFParticularly Pb Graphite useful for Pellets copper Pb Boron Nitride PbNitrogen Foam Granules Particularly B Graphite useful for Pellets copperB, Boron Nitride B Nitrogen Foam Granules Particularly Mixture of BoronNitride useful for Pb PbSO4 and Nitrogen Foam aluminum USO GranulesParticularly Mixture of Graphite useful for Pb PbSO4 and Pelletsaluminum U504 12. A structure for controlling the location of asolidliquid interface in a nozzle into which liquid metal iscontinuously entering and from which solid metal in a given shape isbeing withdrawn comprising a plurality of layers of fused compounds,each higher layer being of lower melting point than the layer below itso that heat flows from said nozzle to the uppermost layer and eachhaving a substantial thickness sufficient to cool molten metal passingthrough said nozzle means.

13. A structure as in claim 12 wherein said layers are chosen from thegroup consisting of:

2. An apparatus as in claim 1 wherein said internal cross section variesto account for the volumetric changes in the liquid to solid phasetransformation to improve the density grain orientation and resultingchemical and electrical properties of the product cast.
 3. An apparatusas in claim 2 including means for controlling the temperature of saidmolten liquid.
 4. An apparatus as in claim 3 wherein said temperaturecontrol means includes means for impinging gas flames on said means forconveying said molten metal from said source to said nozzle means.
 5. Anapparatus as in claim 3 wherein said temperature control means includesresistance heating means for heating said conveying means.
 6. Anapparatus as in claim 3 wherein said temperature control means includesan induction heater.
 7. An apparatus as in claim 2 including means forcontrolling the temperature of said nozzle means.
 8. An apparatus as inchaim 2 including means to apply pressure to said liquid metal tocontrol the location of the liquid-solid interface in said nozzle means.9. An apparatus as in claim 8 wherein said pressure control meansincludes means for applying gas pressure to the liquid in said source.10. An apparatus as in claim 8 wherein said pressure control meansincludes means for applying pressure to liquid in said conveying means.11. Apparatus as in claim 1 wherein said layers are chosen from thegroup consisting of: First Second Third Fourth Layer Layer Layer LayerParticularly Pb Bi Mixture of Graphite useful for UF4, PbF Chips steeland LiF Particularly Pb Graphite useful for Pellets copper Pb BoronNitride Pb Nitrogen Foam Granules Particularly B1 Graphite useful forPellets copper B1 Boron Nitride B1 Nitrogen Foam Granules ParticularMixture of Boron Nitride useful for Pb PbSO4 and Nitrogen Foam aluminumPb USO4 Granules Particularly Mixture of Graphite useful for Pb PbSO4and Pellets aluminum USO4
 12. A structure for controlling the locationof a solid-liquid interface in a nozzle into which liquid metal iscontinuously entering and from which solid metal in a given shape isbeing withdrawn comprising a plurality of layers of fused compounds,each higher layer being of lower melting point thAn the layer below itso that heat flows from said nozzle to the uppermost layer and eachhaving a substantial thickness sufficient to cool molten metal passingthrough said nozzle means.
 13. A structure as in claim 12 wherein saidlayers are chosen from the group consisting of: First Layer Second LayerThird Layer Fourth Layer Particularly Pb Bi Mixture of Graphite usefulfor UF4, PbF2 Chips steel and LiF Particularly Pb Graphite useful forPellets copper Pb Boron Nitride Pb Nitrogen Foam Granules ParticularlyB1 Graphite ta useful for Pellets copper B1 Boron Nitride B1 NitrogenFoam B1 Granules Particularly Mixture of Boron Nitride useful for PbPbSO4 and Nitrogen Foam aluminum USO4 Granules Particularly Pb Mixtureof Graphite useful for PbSO4 and Pellets aluminum USO4